.leftBox{
  float: left;
  width: 20%;
  height: 500px;
  max-width: 200px;
  border-right: 1px solid red;
  box-sizing: border-box;
}
.rightBox{
  float: left;
  width: 80%;
}

.activeMenu{
  background-color: #f00;
}
.defaultMenu{
  background-color: rgb(3, 156, 105);
}